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Old 03-20-2012, 10:12 AM   #1
aj_borel01
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Default Is this right??

Bought my 2004 WRX about 4 months ago and I bought it with a prosport boost gauge. At idle it holds a vacume of about 11 or 12 hg. Iv read it should be around 17 to 22. When it down revs it is around 17 but only til about 2000 rpm. Is this a problem?
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Old 03-20-2012, 10:57 AM   #2
redline23
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Idle vacuum can vary. Don't worry about it at 2000 RPM, the engine is either sucking in air or the turbo is starting to spin a little, thus creating some pressure. You should find out what your target boost is, and see if you are hitting that. That is more important in my opinion.
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Old 03-20-2012, 11:05 AM   #3
aj_borel01
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Thanks, when boosting in 2nd or 3rd gear it jumps to about 14 or 15 psi and almost immediately drops to 10 psi and starts climbing again, that's my other question, is that the car limiting it or a bigger problem?
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Old 03-20-2012, 11:14 AM   #4
redline23
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In 2nd you can't really tell because it revs too fast so you might not even hit full boost before you have to shift. If in third at WOT you hit 14/15 PSI and then it drops to 10 and then climbs again, you will definitively feel if the car is limiting since it would probably feel like no power for a bit.
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Old 03-20-2012, 11:24 AM   #5
aj_borel01
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Ok so if it feels like consistent acceleration there's nothing actually 'wrong'?
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Old 03-20-2012, 11:47 AM   #6
redline23
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Not necessarily, but prosport gauges are very cheap. It is possible that everything is fine, but since I can't see and hear your car, which makes it a bit hard to give a definitive answer so I rambled on a bit.

You need to do some logging to make sure everything is really perfect. For the cheapest way you need a laptop and a friend with a tactrix cable. If you want to have your own cable and do not plan to flash the ECU with it, get a $15 vag-com cable. Mine works fine for just reading data form ECU.

To log with romraider check out this link http://www.clubwrx.net/forums/tuning...romraider.html
and there is a ton more information over at the romraider how to forum
http://www.romraider.com/forum/viewt...hp?f=33&t=5384

Of course maybe someone else knows of a way to tell without putting in quite so much work, but I enjoy learning new information.
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Old 03-20-2012, 11:52 AM   #7
aj_borel01
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Thanks for all the help, I'll do a little research to make sure everything is in proper working order.
But thanks again for the input
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Old 03-20-2012, 12:56 PM   #8
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Stock Target boost for a wrx is only
11-12 psi. What mods are done to the car? Do you know if it has been tuned? Or do you have a aftermarket dp with no tune? These are things we need to know to help.

If the former owner had a Cobb Ap tune on it and put the stock dp on with out switching the map back to stock the turbo is beheld back by the restrictive stock dp.

If he took the stage 2 map off and left the aftermarket dp on you could be getting boost creep.

Both of these are bad. We need to know everything that has been done before we can give a good answer.
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Old 03-20-2012, 02:40 PM   #9
aj_borel01
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Everything is stock except the intake and exhaust, I think the gauge is reading high at first due to the fact that it was $50.
Never been tuned and it was put on a dyno for emissions Only. Haha
I'm trying to learn the basics before I dump hours of work into the motor.
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Old 03-20-2012, 03:10 PM   #10
redline23
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Since it is a 2004, you need a tune for the intake and exhaust (assuming exhaust includes downpipe, no tune required just for catback exhaust). Your car is not running happy without a tune.
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Old 03-20-2012, 03:22 PM   #11
aj_borel01
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It is just a catback for now haha
I'm THAT kid haha

Another random question, wouldn't a cat less exhaust mess up the computer Puting fuel in and such. I ask because I helped a friend put a full turbo back on his 07 wagon with headers up and down pipe and no cat, and we just put the sensors in the pipe, it's been like that for a few months and has had no problems, but is that ruining anything?
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Old 03-20-2012, 03:28 PM   #12
redline23
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You will have no problems with a catback. It's not just catless downpipe that is the problem.
You are putting on a downpipe that is bigger and flows better. The turbo will spool faster than the stock map anticipates and you can overboost (even more prone with catless). If you get a tune you can compensate for all that.

The same goes for the intake, the stock map is calibrated for the stock intake with stock piping. The aftermarket intake will not have the exact same airflow as stock, may have some turbulence, may flow faster, may flow slower where the MAF sees the air. So the ECU will read the wrong amount of air going in, and inject the wrong amount of fuel. Again this can be solved with a simple tune (rescaling the MAF).
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Old 03-20-2012, 04:26 PM   #13
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Quote:
Originally Posted by aj_borel01
It is just a catback for now haha
I'm THAT kid haha

Another random question, wouldn't a cat less exhaust mess up the computer Puting fuel in and such. I ask because I helped a friend put a full turbo back on his 07 wagon with headers up and down pipe and no cat, and we just put the sensors in the pipe, it's been like that for a few months and has had no problems, but is that ruining anything?
Your friends engine could already be toast. He just doesn't know it yet. You NEED a tune for a full tbe.
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Old 03-20-2012, 08:06 PM   #14
aj_borel01
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A Subaru dealership wont tune things for you will they?
Cause that's the only thig around here that deals with anything Subaru related that isn't an hour away.
And how big a deal is it if I am running a short ram with no tune?
I could search but since my newbie questions are already being answered..?
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Old 03-20-2012, 08:25 PM   #15
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Your friend isnt smart. KIDS
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Old 03-20-2012, 10:43 PM   #16
rudymcskoody
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Quote:
Originally Posted by aj_borel01
A Subaru dealership wont tune things for you will they?
Cause that's the only thig around here that deals with anything Subaru related that isn't an hour away.
And how big a deal is it if I am running a short ram with no tune?
I could search but since my newbie questions are already being answered..?
No a dealership will not tune your ecu. If you are going to mod your subaru driving an hour away for a tune is something your going to have to real with.

Having a short ram intake and no tune is not a good thing.

Op buy a Cobb Ap. You can find them used for a few hundred bucks. It has a map for intakes and when you go stage 2. You could be causing harm to your motor until you do.
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Old 03-20-2012, 10:49 PM   #17
TwoFifty
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Vacuum at idle should read around 17-22"

If you are that worried about it find where the guage T's in and hook up a vaccum gauge there and see what it reads, compare that to the gauge. The gauge could be inaccurate. Or maybe you have a small vacuum leak.
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Old 03-21-2012, 08:28 AM   #18
quazimoto
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Quote:
Originally Posted by TwoFifty View Post
Vacuum at idle should read around 17-22"

If you are that worried about it find where the guage T's in and hook up a vaccum gauge there and see what it reads, compare that to the gauge. The gauge could be inaccurate. Or maybe you have a small vacuum leak.
This..........and stock boost for a 2.0L WRX is 13.5psi at sealevel. Usually only going to see this WOT in 4th or 5th gear.
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Old 03-21-2012, 10:48 AM   #19
redline23
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Quote:
Originally Posted by aj_borel01 View Post
A Subaru dealership wont tune things for you will they?
Cause that's the only thig around here that deals with anything Subaru related that isn't an hour away.
And how big a deal is it if I am running a short ram with no tune?
I could search but since my newbie questions are already being answered..?
An hour away isn't bad if they do tunes. My closest tuner is either is at least 2.5-3h away. For your level of mods you can get away without a custom tune. Depending on which intake you have, cobb may already have a map for it on their accessport (stage 1 + xxx intake). Make sure to check before you buy, the accessport is expensive. You can get an open source tune which will be considerably cheaper. And if you want a custom tune, you can get an e-tune(through internet).
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Old 03-21-2012, 10:57 AM   #20
the suicidal eggroll
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What altitude are you at? The higher up you go (and the lower the atmospheric pressure drops), the less vacuum you'll get at idle. 17 to 22 is at sea level, and nowhere else. 12 inHg is -6 psig, if you're at 10,000 feet this is perfectly normal. If you're at sea level it's not. Then you just have to ask yourself whether or not you're actually at 12inHg, or if the gauge is just a POS (likely the latter with Prosport).
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Old 03-21-2012, 11:06 AM   #21
aj_borel01
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Quote:
Originally Posted by the suicidal eggroll
What altitude are you at? The higher up you go (and the lower the atmospheric pressure drops), the less vacuum you'll get at idle. 17 to 22 is at sea level, and nowhere else. 12 inHg is -6 psig, if you're at 10,000 feet this is perfectly normal. If you're at sea level it's not. Then you just have to ask yourself whether or not you're actually at 12inHg, or if the gauge is just a POS (likely the latter with Prosport).
I live at 9000 feet so that makes sense?
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Old 03-21-2012, 11:08 AM   #22
the suicidal eggroll
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Yes, that makes perfect sense.
I idle around -8 psig (16 inHg) at 5400 ft, you'd be even lower than that.

Cars idle at a fixed absolute pressure, ours idle around 4 psia. Gauges read in relative pressure compared to atmo. As atmospheric pressure changes, that same 4 psia will appear to be different gauge pressures. At sea level, 4 psia is -10.7 psig. At 5000 feet 4 psia is -8.2 psig. At 9000 feet 4 psia is -6.5 psig. At 30000 feet you'd be idling around 0 psig, lol.

Last edited by the suicidal eggroll; 03-21-2012 at 11:14 AM.
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